For safety improvement on automobiles and automatic driving of automobiles, various sensors such as millimeter-wave radars, infrared laser sensors, cameras, infrared cameras, and ultrasonic sensors are mounted on automobiles. Using those sensors, systems that detect and recognize obstacles around automobiles are being put into practical use. Ultrasonic sensors are particularly used for the sensors that are applied to parking assist systems to detect close-in objects (e.g., refer to Japanese Patent Application Laid-open No. 2009-236776). An example of the conventional ultrasonic sensors transmits ultrasonic waves having high directivity, detects reflected waves from an object (obstacle), and detects the object on the basis of a time period from the transmission of the ultrasonic waves to the reception of the reflected waves.
The conventional ultrasonic sensor uses ultrasonic waves having high directivity, resulting in a detectable range of an object being reduced. For example, when an object near a door of a vehicle is to be detected, a plurality of ultrasonic sensors need to be arranged two-dimensionally on the entire surface of the door. This structure increases a manufacturing cost and causes a problem of deterioration of an exterior design of the portion where the ultrasonic sensors are disposed.
The invention aims to provide an ultrasonic sensor that can prevent deterioration of an exterior design of a portion where the ultrasonic sensor is disposed while a manufacturing cost is reduced.